Match List I with List II

Choose the correct answer from the options given below:

A-IV, B-I, C-II, D-III

The correct answer is option 2. A-IV, B-I, C-II, D-III.

Let us go through each type of defect in detail and match them with the correct descriptions:

A. Impurity defect: IV. \(NaCl\) with \(Sr^{2+}\) and cationic sites vacant

An impurity defect occurs when a foreign atom (impurity) replaces or occupies a position in the crystal lattice of a host material. There are two types of impurity defects:

Substitutional: Where an impurity atom replaces a host atom in the lattice.

Interstitial: Where an impurity atom occupies an interstitial site in the lattice.

A common example of an impurity defect is found in sodium chloride (NaCl) when a small amount of strontium chloride (SrCl₂) is added. In this case:

\( \text{Sr}^{2+} \) ions substitute \( \text{Na}^{+} \) ions in the NaCl lattice.

To maintain electrical neutrality, for every \( \text{Sr}^{2+} \) ion that enters the lattice, two \( \text{Na}^{+} \) ions are displaced. This creates one vacancy in the cationic site, as only one \( \text{Sr}^{2+} \) ion replaces two \( \text{Na}^{+} \) ions.

B. Metal excess defect: I. \(NaCl\) with anionic sites called F centres

A metal excess defect occurs when there are more metal ions than are required to maintain the stoichiometric composition of the compound. This often happens due to:

Anionic Vacancies (F-Centers): In crystals like \( \text{NaCl} \), some chloride ions (\( \text{Cl}^{-} \)) might be missing from their lattice sites, leaving behind vacancies. These vacancies can trap electrons, and these electron-filled vacancies are called F-centers (from the German word "Farbe," meaning color). The presence of F-centers imparts color to the crystal (e.g., yellow in NaCl).

C. Metal deficiency defect: II. \(FeO\) with \(Fe^{3+}\)

A metal deficiency defect occurs when there are fewer metal ions than are required to maintain the stoichiometric composition. This often happens in compounds where the metal can exist in multiple oxidation states, like in:

Iron oxide (FeO): The formula of iron oxide is typically non-stoichiometric, meaning it doesn't have a perfect ratio of iron to oxygen. For example, some \( \text{Fe}^{2+} \) ions might be missing from the lattice and are replaced by \( \text{Fe}^{3+} \) ions to maintain charge neutrality. However, this still results in a deficiency of metal cations overall.

D. Simple vacancy defect: III. Non ionic solids and density of solid decreases

A simple vacancy defect occurs when an atom or ion is missing from its normal lattice site. This type of defect is common in all kinds of crystalline solids, particularly:

Non-ionic Solids: In these solids, the absence of atoms from the lattice sites creates vacancies, leading to a decrease in the density of the solid since there are fewer atoms in the same volume. This kind of defect doesn't involve any charge balance considerations, as in ionic crystals.

Summary:

1. A-IV: Impurity defect is exemplified by \( \text{NaCl} \) with \( \text{Sr}^{2+} \), where cationic sites are vacant due to the substitution of \( \text{Na}^{+} \) by \( \text{Sr}^{2+} \).

2. B-I: Metal excess defect is illustrated by \( \text{NaCl} \) with anionic vacancies (F-centers), where chloride ions are missing, and electrons occupy the vacant sites.

3. C-II: Metal deficiency defect is found in \( \text{FeO} \), where some \( \text{Fe}^{2+} \) ions are missing, and \( \text{Fe}^{3+} \) ions are present.

4. D-III: Simple vacancy defect occurs in non-ionic solids, where the absence of atoms from the lattice sites decreases the density of the solid.

The correct option is 2. A-IV, B-I, C-II, D-III.